The present invention relates to a combined cycle plant where a gas turbine and a steam turbine are coupled on a single shaft and the steam turbine is a reheating, type steam turbine.
With reheating-type plants of related single shaft combined cycle plants, in that disclosed in, for example, Japanese Patent Laid-open Publication No. Sho. 62-101809, steam provided to a high-pressure turbine bypasses the high-pressure turbine and is supplied to the reheating turbine. The high-pressure turbine is then made to communicate with a condenser and heating accompanying windage loss of high-pressure turbines and reheating turbines at the time of activation of the steam turbine is prevented.
There are cases where steam supplied to a high pressure turbine is superheated by a reheater of an exhaust heat recovery boiler and supplied to a reheating turbine due to the influence of activation conditions, etc. When unit capacity is increased in a single shaft combined cycle plant, output of a steam turbine also rises in accompaniment with increases in output of a gas turbine and the influence of accompanying heat generated due to windage loss occurring due to the rotor blades of the steam turbine being long is substantial.
The object of the present invention is to provide a single shaft combined cycle plant and single shaft combined cycle plant activating method capable of suppressing the influence of steam superheated by the exhaust heat recovery boiler at the time of activation of a reheating type single shaft combined cycle plant and capable of providing stability while suppressing the influence of windage loss of the high pressure turbine and the reheating turbine.
In a first characteristic of the present invention, a single shaft combined cycle plant comprises a gas turbine, an exhaust heat recovery boiler for generating steam using exhaust heat discharged from the gas turbine; and a steam turbine driven by steam generated from the exhaust heat recovery boiler, rotors of the gas turbine and rotors of the steam turbine being coupled, and the steam turbine comprising: a high pressure turbine being supplied with and driven by high pressure steam generated at a superheater of the exhaust heat recovery boiler and a reheating turbine supplied with and driven by steam that passes through the high pressure turbine and is reheated by a reheater of the exhaust heat recovery boiler, wherein steam outputted from the high pressure turbine is made to bypass the reheater from a path leading to the reheater of the exhaust heat recovery boiler and is introduced to a path from the reheater leading to the reheating turbine.
As a result, at the time of plant activation the following steps take place.
A first step of activating the gas turbine and causing rotor speed thereof to rise, a second step of supplying gas turbine exhaust gas to the exhaust heat recovery boiler and causing steam to be generated at the exhaust heat recovery boiler, a third step of supplying steam generated at the exhaust heat recovery boiler to the high pressure turbine rotating with the gas turbine and supplying steam that has passed through this high pressure turbine to the reheating turbine via a bypass path connecting a path leading steam outputted from the high pressure turbine to the reheater and a path leading to the reheating turbine from the reheater, a fourth step of supplying steam generated by the superheater to the reheating turbine via the reheater after desired conditions for the steam generated from the exhaust heat recovery boiler are reached and a fifth step of obtaining an output from the steam turbine.
In the present invention, the reheating of steam generated from the exhaust heat recovery boiler before being supplied to the reheating turbine can be suppressed and steam where the superheating due to the windage loss of the reheating turbine has been cooled to an extent can be supplied.
Further, stopping of the turbine due to superheating accompanying the windage loss of the reheating turbine can be suppressed.
In a second characteristic of the present invention:
separately provided steam supplying means supplies steam to the reheating turbine, a steam connecting path connects the third steam path and the first steam path and discharging means discharges steam supplied from the steam supplying means that flows via the reheating turbine and flows through the second steam path to outside of the second steam path.
As a result, at the time of plant activation the following steps take place.
A first step of activating the gas turbine and causing the rotational speed thereof to rise, a second step of supplying gas turbine exhaust gas to the exhaust heat recovery boiler and causing steam to be generated at the exhaust heat recovery boiler, a third step of supplying steam to the high pressure turbine through the reheating turbine and a steam connecting path provided in such a manner as to connect the third steam path and the first steam path; and discharging steam flowing through the second steam path via the high pressure turbine to outside of the second steam path via discharging means provided at the second path, a fourth step of supplying steam generated by the superheater to the reheating turbine via the reheater after desired conditions for the steam generated from the exhaust heat recovery boiler are reached and a fifth step of obtaining an output from the steam turbine.
Cooling steam that has passed through the reheating turbine is therefore reheated at the exhaust heat recovery boiler and the flow of high temperature steam into low temperature reheating piping downstream of the high pressure turbine, that is designed for conventional temperatures is prevented.
In a third characteristic of the present invention:
first discharging means, arranged upstream of a check valve provided at the second steam path, discharges steam within the high pressure turbine to outside of the high pressure turbine, separately provided steam supplying means supplies steam to the reheating turbine, second discharging means discharges steam, that flows through the third steam path after being supplied from the steam supplying means via the reheating turbine, to outside of the third steam path and the second discharging means is positioned downstream from a reheated steam valve provided at the third path for regulating the amount of steam going to the reheating turbine.
As a result, at the time of plant activation the following steps take place.
A first step of activating the gas turbine and causing the rotational speed thereof to rise, a second step of supplying gas turbine exhaust gas to the exhaust heat recovery boiler and causing steam to be generated at the exhaust heat recovery boiler, a third step of discharging steam remaining within the high pressure turbine using a first discharging means, arranged upstream of a check valve provided at the second steam path, for discharging steam within the high pressure turbine to outside of the high pressure turbine, supplying steam to the reheating turbine and the low pressure turbine using separately provided steam supplying means, and discharging steam passing through the reheating turbine and flowing down the third steam path using a second discharging means, arranged at the third steam path, for discharging steam to outside of the third steam path, a fourth step of supplying steam generated by the superheater to the reheating turbine via the reheater after desired conditions for the steam generated from the exhaust heat recovery boiler are reached and a fifth step of obtaining an output from the steam turbine.
Superheating due to windage loss of the high pressure turbine and reheating turbine and steam reheated by the reheater does not flow as high temperature steam into the low temperature reheating piping downstream of the reheating turbine and high pressure turbine.
The present invention described above can also work in an effective manner in cases where operation is temporarily halted and then restarted again after only a brief cessation or cases where a long period of time is required between the starting up of the gas turbine and the ventilating of and the obtaining of an output from the steam turbine for some reason at the time of start up.
The present invention therefore sets out to pay attention to the fact that, due to conditions at the time of start up etc., steam outputted from the high pressure steam turbine is superheated by the exhaust heat recovery boiler and cannot cool turbines superheated due to windage loss at the time of supplying steam to the reheating turbine, in such a manner that superheating due to windage loss can be suppressed in the high pressure turbine and the reheating turbine by preventing this situation.
The reheating type single shaft combined cycle plant is therefore capable of suppressing the influence of superheating of steam by the exhaust heat recovery boiler due to the influence of the activation conditions etc. and providing stability while suppressing the influence of windage loss of the high pressure turbine and the reheating turbine.